Glass fibers arranged in discrete bundle segments, or chopped strands, are widely used for reinforcements for thermosetting and thermoplastic resinous materials.
In some processes, the need for high bundle integrity is extremely important. For example, in the direct blending type of process, thermoplastic resin pellets and chopped strands of glass fibers are air conveyed to various points. Bundles of chopped strands without good integrity tend to disassociate or deteriorate which can cause process disruptions and even a reduction in the strength of the ultimate molded article.
Chopped strands produced by previous methods tend to have a flattened configuration, especially at the ends of bundles having large amounts of coating material theron. Chopped strands produced by the direct or inline process, wherein the glass filaments are concomitantly drawn from molten streams issuing from a feeder and chopped into discrete segments, characteristically but not necessarily, exhibit the flattened cross-sectional shape to a greater extent than strands chopped "off-line" (i.e., from wound packages).
In addition to the general flattening caused by the tension of the strand around the circumference of the cot of the chopper, the pinching action of the cutter roll against the cot roll upon the undried continuous strand to form the chopped strands severely deforms or flattens the bundles at the end regions thereof.
Such a flattened cross-sectional shape of the discrete bundles increases the bundle susceptibility to cracking, separation and fuzz (i.e., single filaments or small bundles projecting from the sides of the bundle).
The present invention provides method and apparatus for producing chopped strands having a hot melt coating thereon, having bundles exhibiting a rounded or compacted cross-sectional shape along substantially the full length thereof.